X．25网是一种（)A．帧中继网B．局域网C．企业内部网D．分组交换网

Examine the description of the EMPLOYEES table:EMP_ID NUMBER(4) NOT NULLLAST_NAME VARCHAR2(30) NOT NULLFIRST_NAME VARCHAR2(30)DEPT_ID NUMBER(2)Which statement produces the number of different departments that have employees with last name Smith？ （）

A. SELECT COUNT (*) FROM employees WHERE last _name=‘smith‘;

B. SELECT COUNT (dept_id) FROM employees WHERE last _name=‘smith‘;

C. SELECT DISTINCT (COUNT (dept_id) FROM employees WHERE last _name=‘smith‘;

D. SELECT COUNT (DISTINCT dept_id) FROM employees WHERE last _name=‘smith‘;

E. SELECT UNIQE (dept_id) FROM employees WHERE last _name=‘smith‘;

oyees in the EMP table. The EMP table contains these columns:LAST NAME VARCNAR2(35) NOT NULLSALARY NUMBER(9,2) NOT NULLCOMMISION_PCT NUMBER(4,2)Which statement ensures that a value is displayed in the calculated columns for all employees？（）

A. SELECT last_name, 12*salary* commission_pct FROM emp;

B. SELECT last_name, 12*salary* (commission_pct,0) FROM emp;

C. SELECT last_name, 12*salary*(nvl(commission_pct,0)) FROM emp;

D. SELECT last_name, 12*salary*(decode(commission_pct,0)) FROM emp;

oyees in the EMP table. The EMP table contains these columns:LAST NAME VARCNAR2(35) NOT NULLSALARY NUMBER(9,2) NOT NULLCOMMISION_PCT NUMBER(4,2)Which statement ensures that a value is displayed in the calculated columns for all employees？ （）

A. SELECT last_name, 12*salary* commission_pct FROM emp;

B. SELECT last_name, 12*salary* (commission_pct,0) FROM emp;

C. SELECT last_name, 12*salary*(nvl(commission_pct,0)) FROM emp;

D. SELECT last_name, 12*salary*(decode(commission_pct,0)) FROM emp;

The EMPLOYEES table has these columns:LAST_NAME VARCHAR2(35) SALARYNUMBER(8,2) HIRE_DATE DATEManagement wants to add a default value to the SALARY column. You plan to alter the table by using this SQL statement:ALTER TABLE EMPLOYEES MODIFY (SALARY DEFAULT 5000);Which is true about your ALTER statement？（）

A.Column definitions cannot be altered to add DEFAULT values.

B.A change to the DEFAULT value affects only subsequent insertions to the table.

C.Column definitions cannot be altered to add DEFAULT values for columns with a NUMBER data type.

D.All the rows that have a NULL value for the SALARY column will be updated with the value 5000.

The EMP table contains these columns:LAST NAME VARCHAR2(25)SALARY NUMBER(6,2)DEPARTMENT_ID NUMBER(6)You need to display the employees who have not been assigned to any department.You write the SELECT statement:SELECT LAST_NAME, SALARY, DEPARTMENT_IDFROM EMPWHERE DEPARMENT_ID = NULL;What is true about this SQL statement？（）

A. The SQL statement displays the desired results.

B. The column in the WHERE clause should be changed to display the desired results.

C. The operator in the WHERE clause should be changed to display the desired results.

D. The WHERE clause should be changed to use an outer join to display the desired results.

The EMPLOYEES table has these columns:LAST_NAME VARCHAR2(35)SALARY NUMBER(8,2)HIRE_DATE DATEManagement wants to add a default value to the SALARY column. You plan to alter the table by using this SQL statement:ALTER TABLE EMPLOYEESMODIFY (SALARY DEFAULT 5000);Which is true about your ALTER statement？（）

A.Column definitions cannot be altered to add DEFAULT values.

B.A change to the DEFAULT value affects only subsequent insertions to the table.

C.Column definitions cannot be altered to add DEFAULT values for columns with a NUMBER data type.

D.All the rows that have a NULL value for the SALARY column will be updated with the value 5000.

The EMP table contains these columns:LAST NAME VARCHAR2(25)SALARY NUMBER(6,2)DEPARTMENT_ID NUMBER(6)You need to display the employees who have not been assigned to any department. You write the SELECT statement:SELECT LAST_NAME, SALARY, DEPARTMENT_ID FROM EMPWHERE DEPARMENT_ID = NULL;What is true about this SQL statement？ （）

A. The SQL statement displays the desired results.

B. The column in the WHERE clause should be changed to display the desired results.

C. The operator in the WHERE clause should be changed to display the desired results.

D. The WHERE clause should be changed to use an outer join to display the desired results.

The PRODUCTS table has these columns:PRODUCT_ID NUMBER(4)PRODUCT_NAME VARCHAR2(45)PRICE NUMBER(8,2)Evaluate this SQL statement:SELECT *FROM PRODUCTSORDER BY price, product _ name;What is true about the SQL statement？ （）

A. The results are not sorted.

B. The results are sorted numerically.

C. The results are sorted alphabetically.

D. The results are sorted numerically and then alphabetically.

oyees in the EMP table. The EMP table contains these columns:Which statement ensures that a value is displayed in the calculated columns for all employees？（）

A. SELECT last_name, 12*salary* commission_pct FROM emp;

B. SELECT last_name, 12*salary* (commission_pct,0) FROM emp;

C. SELECT last_name, 12*salary*(nvl(commission_pct,0)) FROM emp;

D. SELECT last_name, 12*salary*(decode(commission_pct,0)) FROM emp;

The EMPLOYEES table contains these columns:EMPLOYEE_ID NUMBER(4)LAST_NAME VARCHAR2 (25)JOB_ID VARCHAR2(10)You want to search for strings that contain ‘SA_‘ in the JOB_ID column. Which SQL statement do you use？（）

A.SELECT employee_id, last_name, job_id FROM employees WHERE job_id LIKE ‘%SA\_%‘ ESCAPE ‘\‘;

B.SELECT employee_id, last_name, job_id FROM employees WHERE job_id LIKE ‘%SA_‘;

C.SELECT employee_id, last_name, job_id FROM employees WHERE job_id LIKE ‘%SA_‘ ESCAPE "\";

D.SELECT employee_id, last_name, job_id FROM employees WHERE job_id = ‘%SA_‘;